1. Technical Field
This invention relates generally to hydraulic pump nozzles employed to boost the fluid flow and pressure of hydraulic fluid delivered to a hydraulic pump rotating group, such as a hydraulic pump of a vehicle transmission system.
2. Related Art
In a typical automotive hydraulic transmission system, a motor driven pump delivered hydraulic fluid under pressure to the transmission to operate the transmission with the return fluid being fed to the pump in a closed system. A prior hydraulic booster nozzle such as that illustrated at 10 in FIG. 1 is situated at the intake of the pump 11 and receives a primary flow 12 of hydraulic fluid returned from a sump of the transmission into a primary flow channel 13 of the nozzle 10. In this system, a fraction of the high pressure flow delivered by the pump is diverted around the transmission and fed back to the pump as a bypass flow 14 into a bypass channel 15 of the nozzle 10. This relatively high velocity, high pressure bypass flow 14 is fed through a restriction 16, causing the fluid velocity to increase and the pressure to decrease at the restriction. The high velocity bypass stream exits the restriction and becomes a lower velocity, higher pressure flow at the intake of the rotating group of the pump 11 where it recombines with the primary flow 12, resulting in an overall increased flow in pressure of the combined fluid flow 17 to the pump 11.
While hydraulic boost nozzles of the type shown in FIG. 1 perform satisfactorily in boosting the pressure and flow of hydraulic fluid to the intake rotating group of the pump, there is a tendency to build unacceptably high levels of back pressure in the bypass flow line which cannot be tolerated by other parts of the flow system, particularly under heavy loading of the transmission and pump which are the typical cause of the excessive back pressure in the bypass line. Consequently, one designed constraint of current booster nozzles is that the flow constraint and other design characteristics of the flow channels must be such that they produce exceptionably low levels of back pressure in the bypass line under heavy loading of the pump within design limits of the other components of the system. However, designing the nozzle to decrease the back pressure in the bypass line has the effect of decreasing the boosting performance of the nozzle for delivering maximum flow of hydraulic fluid to the rotating group at the intake of the pump.
A booster nozzle constructed according to the present invention overcomes or greatly minimizes the foregoing limitations of prior booster nozzle constructions.
This invention provides a unique apparatus and method for boosting the pressure at the intake of a hydraulic pump, such as a transmission pump of a vehicle. The apparatus and method are particularly suitable for use in continuously variable transmission (CVT) pump applications. They provide reduced back pressure as compared to prior art booster nozzles, while at the same time providing increased fluid flow, and thus pressure, at the intake of the rotating group. This in turn results in improved pump operating performance, such as reduced cavitation and reduced pump noise at high speeds.
According to particularly preferred features of the invention, the apparatus comprises a nozzle body having a primary flow channel for receiving and delivering a primary flow of hydraulic fluid to the pump. The primary flow is fed from a sump and comprises that portion of the return flow necessary to drive the pump rotating group. The nozzle body is formed with a bypass flow channel that receives a bypass flow of hydraulic fluid from the pump. The bypass flows separately from the primary flow upline of the transmission using an appropriate means, such as splitting the return flow using a bifurcated return line leading from an appropriate flow diverter mechanism situated upstream of the transmission, directing the bypass flow to the bypass flow channel of the nozzle body. The bypass flow is restricted through a restriction device within the bypass flow channel, causing the bypass flow velocity to increase and the pressure to decrease at the restriction. The bypass flow exiting the restriction is recombined with the primary flow in close proximity to the intake of the pump rotating group. As the bypass flow exits the restriction, its flow of velocity decreases producing a corresponding increase in pressure at the intake of the pump rotating group, yielding an overall boost in pressure and flow of the combined primary and bypass flows to the pump.
According to a characterizing feature of the invention, a bypass valve communicates with the bypass channel of the nozzle body. This bypass valve is operated to sense the back pressure in the incoming bypass flow. In response to the back pressure exceeding a predetermined control pressure, the bypass valve opens an auxiliary bypass flow channel and diverts a fraction of the incoming bypass flow around the flow restriction device for direct combination with the delivery of the primary flow to the inlet of the pump. By incorporating a bypass valve into the flow system, a booster nozzle can be designed to optimize its boosting performance to the pump without concern for the effects that such optimized boosting performance would have on the back pressure of the incoming bypass line. The bypass valve can be set to relieve the buildup of back pressure at the appropriate control pressure so as to direct a fraction of the bypass flow around the flow restriction so as to maintain the optimum performance of the booster nozzle for delivery of flow to the pump rotating group, while maintaining the back pressure of the bypass flow below the upper threshold limit control pressure of the particular system.
Another advantage of the present invention is that for a given application, a booster nozzle can be provided with increased boosting performance over that of currently available booster nozzles that at the same time maintains the back pressure of the bypass flow within acceptable design limits. In this way, the boosting performance of the booster nozzle does not need to be sacrificed in order to maintain the back pressure of the bypass flow below design limits.
Another advantage of the present invention is that the same basic booster nozzle construction can be used for a number of difference applications having different bypass flow back pressure requirements, by simply replacing, altering or adjusting the bypass valve to set the control pressure of the valve at the appropriate level to maintain the back pressure below the design limit of the particular application. No longer is it necessary to tailor the flow characteristics of each nozzle body to meet the design criteria of each application, particularly with regard to the limitation set by the bypass back pressure.
Another advantage of the present invention is that the bypass valve can work in conjunction with virtually any combination of primary and bypass flow channel and flow restrictor constructions, and thus is insensitive to the particular design of the booster characteristics of the nozzle. Whatever the design, the bypass valve operates to relieve the back pressure by diverting a fraction of the bypass flow around the flow restrictor. Accordingly, the invention has the further advantage of enabling the same basic bypass valve to be utilized in conjunction with various primary and bypass flow channel configurations. It will thus be appreciated that the subject apparatus has built-in flexibility to meet the design criteria of virtually any flow system calling for a booster nozzle at the intake of a pump in order that the performance of the booster nozzle be optimized both in regard to the delivery of boosted flow to the pump and minimal impact to the performance of the remaining components of the flow system through control of the bypass flow back pressure.